Lunatic fringe promotes the lateral inhibition of neurogenesis

Abstract

Previous studies have identified roles of the modulation of Notch activation by Fringe homologues in boundary formation and in regulating the differentiation of vertebrate thymocytes and Drosophila glial cells. We have investigated the role of Lunatic fringe (Lfng) expression during neurogenesis in the vertebrate neural tube. We find that in the zebrafish hindbrain, Lfng is expressed by progenitors in neurogenic regions and downregulated in cells that have initiated neuronal differentiation. Lfng is required cell autonomously in neural epithelial cells to limit the amount of neurogenesis and to maintain progenitors. By contrast, Lfng is not required for the role of Notch in interneuronal fate choice, which we show is mediated by Notch1a. The expression of Lfng does not require Notch activity, but rather is regulated downstream of proneural genes that are widely expressed by neural progenitors. These findings suggest that Lfng acts in a feedback loop downstream of proneural genes, which, by promoting Notch activation, maintains the sensitivity of progenitors to lateral inhibition and thus limits further proneural upregulation.KEY WORDS: Lateral inhibition, Neurogenesis, Neural progenitors, Notch, Fringe, Zebrafish Development 136, 2523Development 136, -2533Development 136, (2009 DEVELOPMENT 2524 differentiating cells in the cerebral cortex in mouse (Ishii et al., 2000). Furthermore, overexpression of Lfng in the chick neural tube was found to increase the number of neurons (de Bellard et al., 2007). These findings raise the possibility that modulation of Notch activity by Fringe homologues regulates neurogenesis in vertebrates.We set out to investigate the role of Lfng in the zebrafish nervous system, in which gene expression studies have suggested potential roles in boundary formation and/or neurogenesis. At early stages, lfng expression occurs at high levels in alternating segments in the hindbrain (Leve et al., 2001;Prince et al., 2001;Qiu et al., 2004), which by analogy with roles in other tissues could underlie boundary formation. In addition, lfng is expressed in dorsoventrally restricted domains in the neural tube (Prince et al., 2001) that could be associated with zones of neurogenesis. We show that Lfng limits neuronal differentiation and is required to maintain progenitor cells. Lfng acts cell autonomously in progenitors to inhibit their differentiation but, surprisingly, is upregulated downstream of proneural genes. We propose that Lfng acts in a feedback loop that maintains the competence of progenitor cells to receive lateral inhibition from differentiating neurons. MATERIALS AND METHODS Zebrafish linesWild-type, mib ta52b Schier et al., 1996), notch1a tp37 (Gray et al., 2001;Holley et al., 2002;van Eeden et al., 1996) and Tg(r3/r5-Gal4::UAS-RFP) embryos were produced and staged according to hours post fertilisation (hpf) and morphological criteria (Kimmel et al., 1995). MicroinjectionBlastomeres (1-to 4-cell) were microinjected with 0.45-1.8 pmol morpholino oligonucleotide (MO; Gene Tools). The ...

Jagged mediates differences in normal and tumor angiogenesis by affecting tip-stalk fate decision

“…Loss of this brake, as seen in aggressive tumors such as basal-like breast cancer (32)(33)(34), can enable tumors to attain sustained angiogenesis (35), which is a hallmark of cancer (44). Overall, our results about Fringe are also consistent with experimental and theoretical observations that Fringe promotes lateral inhibition patterns (19,45) and are reminiscent of how asymmetric modifications of transmembrane ligand-receptor pairs can govern tissue-level pattern formation (46).…”

Notch regulates blastema proliferation and prevents differentiation during adult zebrafish fin regeneration

“…We confirmed these findings using morpholinos (MO) against notch1b, jag1b (Lorent et al, 2004), rbpjκ (Sieger et al, 2003) and lfng (Nikolaou et al, 2009). MOs were injected into the dorsal halves of fins after regeneration for 2 days at 28°C and transfection was induced by electroporation.…”

“…We used the following fluorescein-coupled morpholino oligonucleotides (MO; GeneTools): jag1b, notch1b (Lorent et al, 2004), rbpjκ (Sieger et al, 2003), lfng (Nikolaou et al, 2009) and a standard negative control. MOs were injected and electroporated as described previously (Thummel et al, 2006) into the dorsal half of fins after regeneration for 2 days in water at 28°C.…”

Synthetic lateral inhibition governs cell-type bifurcation with robust ratios

“…Thus, addition of the LF circuit should increase the frequency of cell-type bifurcation and therefore increase the proportion of green cells. In fact, knockout or knockdown of Lfng has been reported to decrease the proportion of Notch-active cells (represented by the green cells in our study) in the developing vertebrate nervous system 36,37 .…”